The present invention relates to a radial-air-gap induction motor used as a fan motor of an air conditioner, particularly to an induction motor having two stators and provided with a two radial air gaps constituted by setting a rotor between the stators.
Most induction motors respectively use the inner rotor type constituted by setting one rotor at the inside of one stator for generating a rotating magnetic field. The stator is provided with windings in order to generate a rotating magnetic field and the rotor is provided with case windings for generating an induced current.
In the case of the above induction motor, when setting the rotor in the rotating magnetic field of the stator, an induced current circulates through the case windings of the rotor, a rotating torque works on the case windings due to the mutual action between the rotating magnetic field and the induced current and thereby, the rotor rotates. This type of the induction motor is frequently used for electrical home appliances and industrial machines from the viewpoints of simplicity and economical efficiency.
In the case of a conventional induction motor, however, a loss tends to increase and an efficiency tends to deteriorate for an output as the motor is further decreased in size and moreover, the trend of the efficiency deterioration becomes stronger as the number of poles of the motor increases.
The relation shown by the following expression (1) is present between efficiency, loss, output, and input.
Efficiency=Output/input=Output/output+Lossxe2x80x83xe2x80x83(1)
Therefore, it is found that a loss should be decreased in order to improve an efficiency. The loss of an induction motor includes the following.
 less than 1 greater than  Primary copper loss (Copper loss; Stator winding resistance loss)
 less than 2 greater than  Secondary copper loss (Rotor winding resistance loss)
 less than 3 greater than  Iron loss (Core loss; Hysteresis loss)
 less than 4 greater than  Iron loss (Eddy current loss)
 less than 5 greater than  Mechanical loss (Bearing loss or windage loss)
 less than 6 greater than  Stray load loss
The primary copper loss in  less than 1 greater than  and the secondary copper loss in  less than 2 greater than  account for a large ratio among the above  less than 1 greater than  to  less than 6 greater than . To reduce these copper losses of a conventional induction motor, it is necessary to use one of a method for reducing a resistance loss by increasing a stator core in size and a groove (slot) area and coiling a winging having a large wire diameter and a method for increasing the outer diameter of a rotor core so that the same torque can be output even by a small induced current. However, these methods are not preferable because the material cost is greatly increased.
In general, the output equation of a motor is shown by the following expression (2).
Output=K1xc2x7D2xc2x7Lxc2x7Bmxc2x7Acxc2x7nxe2x80x83xe2x80x83(2)
In the above expression, K1 denotes a constant, D denotes the diameter of a radial air gap, L denotes the length of a core, Bm denotes the average magnetic-flux density of an air gap, Ac denotes the number of ampere conductors, and n denotes a rotating speed.
In the case of an induction motor, the average magnetic-flux density Bm of an air gap is almost proportional to the number of ampere conductors Ac. Therefore, the above expression (2) can be shown as the following expression (3).
Output=K2xc2x7D2xc2x7Lxc2x7Bm2xc2x7nxe2x80x83xe2x80x83(3)
In the above expression, K2 is a constant.
Then, the relation between a loss and the average magnetic-flux density Bm of an air gap is studied below. A current I is almost proportional to a maximum magnetic-flux density B. The number of ampere conductors Ac is almost proportional to the current I and the average magnetic-flux density Bm of an air gap is almost proportional to the maximum magnetic-flux density B. Therefore, it can be considered that the primary copper loss (current I2xc2x7winding resistance) in the above  less than 1 greater than  almost proportional to Bm2.
Moreover, the secondary copper loss in the above  less than 2 greater than  is equal to (secondary current circulating through a rotor winding)xc2x7secondary resistance and the secondary current is almost proportional to Bm. Therefore, it can be said that the secondary copper loss in the above  less than 2 greater than  is almost proportional to Bm2.
It is publicly known that the iron loss (hysteresis loss) in the above  less than 3 greater than  and the iron loss (eddy current loss) in the above  less than 4 greater than  are almost proportional to B2, that is, Bm2. Because it is estimated that the mechanical loss (bearing loss or windage loss) in the above  less than 5 greater than  and the stray load loss in the above  less than 6 greater than  account for a small rate in the total loss, it can be said that the total loss is almost proportional to Bm2.
To greatly improve an efficiency, it is necessary to minimize losses. Because a loss is almost proportional to the square of the average magnetic-flux density Bm (Bm2) of an air gap, it is necessary to greatly reduce Bm2 in order to greatly reduce the loss. However, because by reducing Bm2, an output is also reduced proportionally to Bm2, it is necessary to use means for compensating the output.
As a method for realizing the above mentioned, it is possible to keep an output constant because (Bm2)xc3x97(D2xc2x7L) becomes constant by increasing the square of (diameter D of radial air gap)xc3x97core length L by a value equivalent to the decrease of Bm2. However, it is uneconomic to increase (D2xc2x7L) in a conventional induction motor because a core size (constitution) increases.
Therefore, it is a problem of the present invention to greatly improve the efficiency of an induction motor without increasing the core size (constitution).
To solve the above problem, the present invention uses an induction motor having a radial air gap, which is constituted so as to have a two air gaps and in which windings for generating a rotating magnetic field for the above rotor is set to the above outer and inner stators, and squirrel-cage windings are set to the rotor.
Thus, by forming the radial air gaps and maximizing the diameter of each air gap, it is possible to greatly increase (D2xc2x7L). Therefore, it is also possible to greatly reduce Bm2 and thereby greatly reduce losses. Therefore, it is possible to improve an efficiency without increasing the core size (constitution). The output equation when forming the radial air gaps is shown by the following expression (4).
Output=K2xc2x7(Do2+Di2)xc2x7Lxc2x7Bm2xc2x7nxe2x80x83xe2x80x83(4)
In the above expression, Do denotes the diameter of the outer radial air gap and Di denotes the diameter of the inner radial air gap.
It is preferable that the number of slots of the outer stator is equal to or different from the number of slots of the inner stator and the number of slots of the above rotor is equal to prime numberxc3x972 or prime numberxc3x974. Thereby, a squirrel-cage winding rotor becomes suitable for an induction motor.
It is preferable to make the pitch between windings applied to the inside of the above outer stator equal to or different from the pitch between windings applied to the outside of the above inner stator. Thereby, an induction motor suitable for a purpose is realized.
According to the present invention, it is possible to realize a capacitor induction motor in which an induced current circulates through the squirrel-cage windings of a rotor in accordance with a rotating magnetic field generated in each stator by applying the same numbers of or different numbers of slots to the above outer and inner stators, relatively shifting a spatial phase angle by xcfx80/2 in terms of an electrical angle, applying main windings and auxiliary windings to the teeth formed at the inside of the outer stator in the form of a concentrated windings, applying a main windings and an auxiliary windings to the grooves formed at the outside of the inner stator in the form of a distributed winding or concentrated winding, and generating a rotating magnetic field in each stator.
In FIGS. 4 to 6, according to the present invention, a main windings and auxiliary windings are alternately applied to teeth constituting 12 slots of the above outer stator and the main windings and the auxiliary windings are connected in series so that the adjacent main and auxiliary windings generate magnetic fluxes opposite to each other.
Three main windings and three auxiliary windings at a two-slot pitch are sequentially applied to grooves constituting 12 slots of the above inner stator every other slot so that the main windings and auxiliary windings are provided by being shifted by one slot from each other, and the main and auxiliary windings are connected in series so as to generate same-directional magnetic fluxes.
Then, a six-pole capacitor induction motor is obtained by connecting the main windings of the outer stator with those of the inner stator in series so as to be used as the main windings of the capacitor induction motor and connecting the auxiliary windings of the outer stator with that of the inner stator in series so as to be used as the auxiliary windings of the capacitor induction motor.
Moreover, it is possible to realize a capacitor induction motor in which an induced current circulates through the squirrel-cage windings of the above rotor by applying the same number of slots to the above outer stator and inner stator, making the teeth formed at the inside of the outer stator face the teeth formed at the outside of the inner stator, and applying a main winding and auxiliary winding to each tooth of the outer and inner stators in the form of a concentrated winding to generate a rotating magnetic field in each stator.
In FIGS. 9 to 11, according to the present invention, six main windings and six auxiliary windings are alternately applied to teeth constituting 12 slots of the above outer stator and six main windings and six auxiliary windings are alternately applied to teeth constituting 12 slots of the above inner stator the same as the case of the outer stator.
Then, the auxiliary windings of the outer stator and those of the inner stator are connected in series so that the windings generate the same-directional magnetic fluxes and directions of magnetic fluxes generated by the adjacent auxiliary windings are opposite to each other.
Then, the auxiliary windings of the outer stator and those of the inner stator are connected in series so that the windings generate the same-directional magnetic fluxes and magnetic fluxes generated by the adjacent auxiliary windings are faced to each other.
Thereby, a six-pole capacitor induction motor can be obtained by using the main windings of the outer and inner stators connected in series as the main windings of the capacitor induction motor and the auxiliary windings of the outer and inner stators connected in series as the auxiliary winding of the capacitor induction motor.
A three-phase induction motor in which an induced current circulates through the squirrel-cage windings of the above rotor is realized by applying the same number of slots to the above outer and inner stators, making the teeth formed at the inside of the outer stator face the teeth formed at the outside of the inner stator and applying three-phase windings to the teeth of the outer and inner stators in the form of a concentrated winding to generate a rotating magnetic field.
In FIGS. 12 to 14, according to the present invention, a three-phase winding is sequentially applied to each tooth of the above outer stator and a three-phase winding same as the case of the outer stator is sequentially applied to each tooth of the above inner stator.
For windings at these phases, the winding of the outer stator and those of the inner stator are alternately connected to each other in series and the windings of the outer stator and the windings of the faced inner stator are set so as to generate the same-directional magnetic fluxes and so that opposite-directional magnetic fluxes are generated by adjacent windings. By Y-connecting the windings at the phases connected in series, a three-phase induction motor can be obtained.
It is preferable to insulate cores of the above outer and inner stators and then, maintain a coil or insert the coil into a slot by an inserter, or directly apply a winding to a tooth, or apply a toroidal winding to the yoke portion of a stator. Thus, by using a winding suitable for the characteristic of an induction motor, an optimum induction motor is obtained.
It is preferable to constitute the above rotor by a core having at least teeth and a slot and a squirrel-cage winding formed through the slot, constitute the core by automatically laminating electromagnetic steel plates in the axial direction of a rotor shaft in a press die, and form a squirrel-cage winding on the slot by a conductive metal. Thereby, it is possible to manufacture an induction motor by using a conventional manufacturing system and prevent the cost from rising.
It is preferable to integrally solidify the above outer and inner stators respectively provided with windings with a thermosetting resin and fix them to the inside of a bracket. Moreover, it is preferable to fix the above outer stator to the inner diameter fitting portion of the bracket and the above inner stator to the inner face of the bracket or the bearing housing portion of the shaft by a holding portion. Thereby, the reliability of the induction motor is improved because the stators are securely fixed to the bracket.
In the case of the slot of the above rotor core, the outer end or inner end is formed into an open shape or both the outer and inner ends are formed into an open shape or closed shape. When either or both of them is or are formed into an open shape, a part of a core laminated sheet is formed into a closed slot. Thereby, because not-continuous independent teeth are formed on the rotor, a magnetic flux is effectively used and the efficiency of the motor is improved.
In the case of the above rotor, by casting an aluminum die-cast in a slot and forming squirrel-cage windings so that it is integrated with an end rings and applying a joint to at least one-hand end ring and fixing the joint to a rotor shaft, it is possible to easily manufacture the squirrel-cage windings and cut the cost.
Moreover, by forming cores of the above rotor into open slots and connecting all teeth each other by a ring arm, magnetic fluxes are concentrated on the teeth and a magnetic-flux density is raised and therefore, an efficiency can be further improved.